1. Technical Field
The field of art to which the invention pertains may be generally located in the class of devices relating to valves. Class 137, Fluid Handling, U.S. Patent Office Classification, appears to be the applicable general area of art to which the subject matter similar to this invention has been classified in the past.
2. Background Information
This invention relates generally to air valves, and more particularly, to a three-way, normally closed, pilot air valve for use in controlling the flow of pilot air to a directional flow control valve for operating the main spool valve thereof. The type of directional flow control valve which may be controlled by the pilot air valve of the present invention includes four-way valves, three-way valves, two-way valves, and the like. A three-way normally closed, pilot air valve includes a captive poppet valve spool which is movably mounted in a valve bore formed directly in a valve body, or in a valve retainer member mounted in the valve body, and which is movable between a closed position and an open position. The captive poppet valve spool has an upper conical annular, poppet valve member element adapted to be seated on a first sharp edged circular valve seat when the poppet captive valve spool is in the inoperative or closed position, and a lower conical annular, poppet valve member element adapted to be seated on a second sharp edged circular valve seat when the captive poppet valve spool is in the operative or open position. Examples of prior art pilot air valves are shown in U.S. Pat. Nos. 4,100,519, 4,271,868, 4,298,027 and 4,407,323.
A problem encountered with the use of a captive poppet valve spool in a pilot air valve of the aforementioned type, is that the captive poppet valve spool is moved from an inoperative or closed position to an operative or open position by an electrical solenoid which shifts the captive poppet valve spool at a high speed, and the lower conical annular, poppet valve member element on the captive poppet valve spool hits its respective sharp edged seat at a high rate of speed, whereby after a period of use the lower conical annular, poppet valve member element is cut, abraded, and parts of it are sheared off. The captive poppet valve spool is returned to the inoperative or closed position after the solenoid is de-energized by a return spring, but the return movement of the captive poppet valve spool is a slow movement compared to the movement in the opposite direction when the solenoid is energized to move the captive poppet valve spool from the inoperative or closed to the operative or open position. Attempts have been made to overcome the aforementioned problem by making the conical annular, poppet valve member elements on the captive poppet valve spool from elastomeric materials which are tough materials, and resistant to abrasion, such as urethane. However, during use, urethane reverts back to a gum stage, due to water and oil mixes or emulsions, which a valve may be subjected to during use. There is water and oil in pneumatic or air systems and these elements also cause the urethane to swell. The use of a nitrile compound which is much more resistant to oil and water than a urethane compound has been used to provide the elastomeric material for the conical annular, poppet valve member elements on a captive poppet valve spool of this type. However, a nitrile compound is not as tough and abrasion resistant as urethane.